#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LEN 40

int main(int argc, char **argv) {
    FILE *in, *out;
    int ch;
    char name[LEN];
    int count = 0;
    if (argc < 2) {
        fprintf(stderr, "No Parameters!\n");
        exit(EXIT_FAILURE);
    }
    if ((in = fopen(argv[1], "r")) == NULL) {
        fprintf(stderr, "Open source file fail!\n");
        exit(EXIT_FAILURE);
    }
    strncpy(name, argv[1], LEN - 5);
    name[LEN - 5] = '\0';
    strcat(name, ".red");
    if ((out = fopen(name, "w")) == NULL) {
        fprintf(stderr, "Open dest file fail!\n");
        exit(EXIT_FAILURE);
    }
    while ((ch = getc(in)) != EOF) {
        if (count++ % 3 == 0) {
            putc(ch, out);
        }
    }
    if (fclose(in) != 0 || fclose(out) != 0) {
        fprintf(stderr, "Close file fail!\n");
        exit(EXIT_FAILURE);
    }
    return 0;
}